This invention relates to multicast routing.
Multicast routing enables a host to transmit a stream of data packets to a group of hosts on a wide area network (WAN). Each multicast data packet has a multicast group address, which functions like a radio channel. Hosts tune into the multicast packet by joining the associated multicast group address. While a host belongs to the multicast group, the host receives each data packet transmitted to the multicast group address.
A multicast router records memberships to multicast group addresses by hosts of the local area network (LAN""s) to which the multicast router connects. From these memberships, a multicast router determines whether to transmit received multicast packets to LAN""s to which the router connects.
A multicast router may dynamically update memberships so that hosts can join and quit multicast group addresses. Dynamically updating enables hosts to tune in and out of multicast data traffic.
The Internet Group Management Protocol (IGMP) provides one process for dynamically updating memberships to multicast group addresses. The IGMP process entails making regular queries to LAN hosts supporting the IGMP protocol. An IGMP querying router queries a LAN to which it connects at regular intervals, e.g., once a minute. In response to a query, an IGMP host transmits one or more messages reporting its memberships to multicast group addresses.
The routing algorithm determines the detailed routing of multicast data packets. One routing algorithm uses the link state routing protocol. To perform the link state routing protocol, routers regularly collect delay or cost data for sending packets to adjacent routers. From the collected data, the routers construct packets with local routing data. The local routing data includes memberships to multicast group addresses. The routers flood the packet with the local routing data to other routers of the network. To implement flooding, each router transmits an incoming packet to every outgoing line of the router except the line on which the packet arrived. The routers receive similar packets from the other routers and use the received packets to calculate future routings for data packets, e.g., multicast data packets.
Routing protocols use hierarchical organization to improve performance of the link state routing algorithm on large networks. One such routing protocol is the open shortest path first (OSPF) protocol. In the OSPF protocol, a special set of routers, i.e., designated routers (DR), collect and disseminate the local routing data to the OSPF routers. Limiting these activities to DR routers reduces network traffic and calculations for determining future routings.
In a first aspect, the invention provides an apparatus. The apparatus includes a router configured with a static membership to a multicast group address. The router is capable of transmitting a message reporting the static membership to another router.
In a second aspect, the invention provides a method of propagating memberships to multicast group addresses. The method includes transmitting a message reporting one or more static memberships to multicast group addresses. The message is transmitted from a first multicast router configured with the one or more static memberships to a second multicast router.
Various embodiments propagate memberships to multicast group addresses of statically configured routers. Corresponding multicast data packet traffic is received by local area networks connected to such routers.